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Abnormally expanded DNA repeats are associated with several neurodegenerative diseases. In Friedreich's ataxia (FRDA), expanded GAA repeats in intron 1 of the frataxin gene (FXN) reduce FXN mRNA levels in averaged cell samples through a poorly understood mechanism. By visualizing FXN expression and nuclear localization in single cells, we show that GAA-expanded repeats decrease the number of FXN mRNA molecules, slow transcription, and increase FXN localization at the nuclear lamina (NL). Restoring histone acetylation reverses NL positioning. Expanded GAA-FXN loci in FRDA patient cells show increased NL localization with increased silencing of alleles and reduced transcription from alleles positioned peripherally. We also demonstrate inefficiencies in transcription initiation and elongation from the expanded GAA-FXN locus at single-cell resolution. We suggest that repressive epigenetic modifications at the expanded GAA-FXN locus may lead to NL relocation, where further repression may occur.

Original publication

DOI

10.1093/hmg/ddv096

Type

Journal article

Journal

Hum Mol Genet

Publication Date

15/06/2015

Volume

24

Pages

3457 - 3471

Keywords

Alleles, Cell Line, Gene Expression, Gene Order, Gene Silencing, Genetic Loci, Humans, Iron-Binding Proteins, Nuclear Lamina, Protein Transport, RNA, Messenger, Single-Cell Analysis, Transcription Initiation Site, Transcription Initiation, Genetic, Transcription, Genetic, Trinucleotide Repeat Expansion